IGCSE Chemistry: States of Matter – Answers #
Focus Questions #
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Answer:
- A solid has a fixed shape and volume
- A liquid has a fixed volume but its shape changes to that of the container in which it is placed
- A gas has no fixed shape or volume. A gas completely fills the container that it is in
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Answer: Draw particles in the boxes:
- Solid: Particles close together in regular rows
- Liquid: Particles close together but randomly arranged
- Gas: Particles far apart and randomly scattered
Practice Questions #
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Answer:
- a) a solid: B
- b) unlikely to be a real substance: C
- c) a gas: A
- d) a liquid: D
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Answer:
- A: melting
- B: freezing
- C: evaporation
- D: condensation
Challenge Questions #
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Answer:
a) Radon
b) Radon and Nitrogen
c) Nitrogen
d) Cobalt
e) The boiling point is higher than expected. This could be due to impurities in the sample.
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IGCSE Chemistry: Cooling Curves & Diffusion – Answers #
Plotting a Cooling Curve #
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Answer: Draw points on the graph. Connect with a smooth curve going down from 96.1°C to 47.0°C.
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Answer: Use hotter water bath (over 100°C)
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Answer: Freezing
Practice Questions #
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Answer: Temperature stays the same because the liquid is changing to solid. Energy goes out but temperature does not change until all liquid becomes solid.
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a) Answer: Draw a curve going down with a flat part in the middle where freezing happens.
b) Answer: The flat part shows freezing. Temperature stays same when liquid becomes solid.
Challenge Questions #
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a) Answer:
- A: solid
- B: melting
- C: liquid
- D: boiling
b) Answer: 17°C
c) Answer: 115°C
d) Answer: Temperature stays the same
e) Answer: This is not water. Water melts at 0°C and boils at 100°C.
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a) Answer: High pressure inside makes carbon dioxide liquid when you shake it.
b) Answer: Hoar frost is a powdery white frost caused when solid ice forms from humid air. The solid surface must be colder than the surrounding air. Water vapor becomes ice without going through the liquid phase.
c) Answer:
Evaporation: Happens at surface only. Can happen at any temperature. Only fast particles escape.
Boiling: Happens everywhere in the liquid. Only at boiling point. Bubbles form inside liquid.
Dissolving and Diffusion #
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a) Answer: Particles from the crystal surface spread out in water. The particles move and mix. The solid dissolves completely. The purple color evenly spread everywhere.
b) Answer: Faster. Hot water makes particles move quicker.
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Answer: Sublimation
